A. Field of the Invention
The present invention relates generally to torque-limiting apparatus and more particularly to a hydraulically operated apparatus with recording means.
B. Description of the Prior Art
In the oil and gas well drilling and completion industries, sections of pipe are connected together to form long strings. Sections of drill pipe are connected together by means of tool joints, which comprise a pin and box. Casing is normally assembled by means of casing collars, which are short sections of pipe having female threads at both ends. Both drill pipe and casing are normally made up with mechanical devices known as power tongs, which are normally hydraulically-operated torque-applying devices.
The torque applied in making up sections of pipe must be carefully controlled in order to prevent too much torque from being applied to the pipe and the possible consequent twisting off of the pipe or stripping of the threads. If the threads become stripped, then it is distinctly possible that the string of pipe can be dropped into the hole, thereby necessitating a costly fishing job.
Normally, the operator requires that a record be kept of the torque applied to each connection. The torque is measured by means of a hydraulic tension cell placed between the power tongs and a fixed attachment. The torque is proportional to the hydraulic pressure generated in the cell and hydraulic recording means are provided that convert pressure and record torque. The record of torque applied is useful in determining whether a mishap is due to operator error or defective pipe. However, having a record that the lost pipe was caused by excessive torque does not eliminate the fishing job.
Accordingly, it is an object of the present invention to provide a recording apparatus with means for limiting the torque applied to the pipe.